Typical direct injection engines either have a centrally mounted fuel injector aimed at the piston crown or a side mounted injector aimed at the cylinder bore wall. These designs have the problem of significant piston crown fuel wetting or cylinder wall fuel wetting.
In accordance with the present invention, a side mounted fuel injector is aimed at the exhaust valve. All of the fuel that is not vaporized before reaching the exhaust valve, which may be on the order of about 10%, will be instantly vaporized when the droplets impinge on the exhaust valve. This eliminates fuel wetted surfaces and the resulting diffusion flame combustion.
In the case of late injection and lean stratified charge, this should result in low hydrocarbon emissions and more favorable burn rates than direct injection spark ignition engines with wall wetting. In the case of early injection and homogeneous charge, the relationship between the fuel injector and the air inlet stream promotes very good air/fuel mixing. In addition, the fuel cooling of the exhaust valve may yield an improvement in knock resistance.
In accordance with the embodiment of the invention about to be described, the fuel injector is positioned to direct a plume of fuel into the combustion chamber along a path and in a direction to impinge upon the exhaust valve. The piston has an end face formed with a concave recess or pocket. The exhaust valve is constructed and arranged to deflect fuel impinging thereon into the recess. The recess is shaped to redirect fuel back toward the path of the plume of fuel.
More specifically, the plume of fuel from the injector has a marginal portion intersecting the spark plug gap. The fuel that is redirected back towards the path of the plume of fuel from the injector is directed toward the spark plug gap.
In accordance with the present construction, the widest part of the injection plume intersects the spark plug gap. This provides an opportunity for ignition very shortly after injection. Also, the liquid fuel that reaches the hot exhaust valve surface vaporizes on contact with this surface at a point which is a very short distance from the spark plug gap and provides another opportunity for ignition. Liquid fuel and vapor which bounces, spatters, or is simply deflected from the surface of the exhaust valve and is guided by the recess or pocket in the piston top back towards the spark plug gap provides yet another opportunity for ignition. If ignition is accomplished before this redirected fuel reaches the spark plug gap, it will intersect the expanding flame front and be quickly burned.
One object of this invention is to provide an exhaust-valve-targeted combustion chamber design for a direct injection spark ignition engine having the foregoing features and capabilities.
Another object is to provide an exhaust-valve-targeted combustion chamber design which is of relatively simple construction yet highly effective in the performance of its intended function.
Other objects features and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings.